By Michelle Wheater
On October 19, 2017, an asteroid from interstellar space passed by Earth. The asteroid, named ‘Oumuamua is the first interstellar object to enter our solar system in recorded history. The interstellar object was spotted by the Pan-STARRS 1 telescope in Hawaii. ‘Oumuamua’s arrival did not make the news until this year when the Harvard Smithsonian Center for Astrophysics published a paper analyzing ‘Oumuamua’s trajectory and making some exciting hypothesis about where it came from.
‘Oumuamua did not follow a Keplerian trajectory, a trajectory in which an object forms an ellipse, a parabola, or a hyperbola around another object based on their gravitational interactions. The trajectory that ‘Oumuamua took around the sun was statistically significant from the usual Keplerian trajectory (Bialy and Loeb 2018). ‘Oumuamua took a path that would be expected of a comet. A comet's path is not that of a Keplerian trajectory because comets outgas, a process in which the ice on a comet melts as it gets closer to the sun and the trapped gas within the ice is released, pushing the comet away from the sun. But ‘Oumuamua is not a comet, it did not have a cometary tail and did not experience any outgassing (Bialy and Loeb 2018). Solar radiation pressure, the force from the solar radiation hitting it, could be to blame for ‘Oumuamua’s trajectory (Bialy and Loeb 2018).
Another peculiar aspect of ‘Oumuamuais was its long and skinny shape. It was proven that “very thin objects can travel over galactic distances, maintaining its momentum and withstanding collisional destruction by dust grains and gas, as well as centrifugal and tidal forces” (Bialy and Loeb 2018). But ‘Oumuamua still has an unusually small mass-to-area ratio, raising questions on what type of object it is. Other objects in the solar system have a “mass-to-area ratios orders of magnitude” larger than our estimate for ‘Oumuamua [and if] radiation pressure is the accelerating force, then ‘Oumuamua represents a new class of thin interstellar material, either produced naturally… or of an artificial origin” (Bialy and Loeb 2018).
Based around these unusual findings the authors suggested that ‘Oumuamua could possibly be a lightsail, a method for propulsion in space that uses solar radiation pressure, from debris in interstellar space (Bialy and Loeb 2018). They also said that it could possibly be “a fully operational probe sent intentionally to Earth vicinity by an alien civilization”; although they did call this an “exotic scenario” (Bialy and Loeb 2018). Overall, the paper never came to any conclusions about why ‘Oumuamua exhibited such unusual properties and trajectory. They were not saying that this definitely was, or was part of, a alien spacecraft, they just said that it could possibly be. We will never really know what ‘Oumuamua was. By the time that this paper came out ‘Oumuamua was already out of range of any telescopes that could have taken a closer look at it. Unless ‘Oumuamua comes back into our solar system, we can only guess about its origins.
Bialy, S., & Loeb, A. (2018). Could Solar Radiation Pressure Explain ‘Oumuamua’s Peculiar Acceleration?. The Astrophysical Journal Letters, 868(1), L1.
Beatty, K. (2017, November). Update on `Oumuamua, Our First Interstellar Object. https://www.skyandtelescope.com/astronomy-news/update-on-interstellar-object-oumuamua/.
Reid, R. (2018, November). Nailing down the nature of ‘Oumuamua—it’s probably a comet, but.... https://arstechnica.com/science/2018/11/nailing-down-the-nature-of-oumuamua-its-probably-a-comet-but/.